For best results, you want to rotoscope, by which I mean every frame. This is best when dealing with fast motions. Keyframing can work, but not always. You could try keyframing the major turning points, then go in and rotoscope whenever the keyframes don’t match up. It’s really your choice.

Well, all these tutorials use AE 5.5, I’m using 4.1, which (I think) means that I cannot edit or create masks on the comp-window itself, I have to open the layer itself in a window before I can do it… This means that its hard to change the postion of the mask, and when I try to do in on the solid-layer itself, I don’t see where the sabers are… 😡

1. Make a new composition and put your raw footage in it.
2. Make a second composition, identical to the first. (Then make this new comp at least 10 pixels larger on all sides than Comp 1. Don’t adjust the footage size, though.)
3. Double-click the footage layer. It’ll open in a separate window.
4. Draw your mask on it, frame-by-frame. Add your fanning, if necessary. Don’t forget to click the little clock icon for keyframes next to Mask Shape before you draw more than one mask. (Draw the mask beyond the edges of the footage, if parts of the saber go out of frame.)
5. When you’re all done, close that window. Your second composition should now look like a ‘disembodied’ saber blade.
6. Make a white solid, the same size as the comp. Put it under the floating saber footage.
7. Under Switches/Modes, turn on a TrkMat (trackmat) for the solid. Pick Alpha Matte. Turn off the eye (visibility) icon for the saber footage. Now you have a ‘disembodied’ white shape that moves like your saber.
8. Go to Comp 1. Drag Comp 2 in on top of your raw footage. (It’s better to drag into the timeline window, so it automatically centers.)
9. Blur the solid. Add the coloured glow. (This is why Comp 2 to needs to be bigger and the mask drawn over the edges. If you don’t, the feathering will be a problem near the edges of the frame.)
10. Done! Although… if your saber goes behind things, it’s a whole other level of rotoscoping. To do it right, you need another composition where you add the blur and glow before bringing it into Comp 1, otherwise the blur and glow will extend over the foreground object. If all the above makes sense to you, though, you should be able to figure it out.